如何通过MongoDB中子文档上的条件查询文档？
首先让我们创建一个包含文档的集合-
> db.demo394.insertOne(
... {
...
... details: [
... {
... _id: '1',
... startDate: '2018-01-11T07:00:00.000Z',
... endDate: '2019-01-12T07:59:59.999Z'
... },
... {
... _id: '2',
... startDate: '2019-01-21T07:00:00.000Z',
... endDate: '2020-01-04T07:59:59.999Z'
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5e716817aa3ef9ab8ab202")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo394.find();
这将产生以下输出-
{
"_id" : ObjectId("5e5e716817aa3ef9ab8ab202"), "details" : [
{ "_id" : "1", "startDate" : "2018-01-11T07:00:00.000Z", "endDate" : "2019-01-12T07:59:59.999Z" },
{ "_id" : "2", "startDate" : "2019-01-21T07:00:00.000Z", "endDate" : "2020-01-04T07:59:59.999Z" }
]
}以下是如何通过子文档上的条件查询文档-
> db.demo394.find({
... $expr: {
... $let: {
... vars: { "d": { $arrayElemAt: [ "$details", -1 ] } },
... in: { $eq: [ "$$d.endDate", "2020-01-04T07:59:59.999Z" ] }
... }
... }
... })这将产生以下输出-
{
"_id" : ObjectId("5e5e716817aa3ef9ab8ab202"), "details" : [
{ "_id" : "1", "startDate" : "2018-01-11T07:00:00.000Z", "endDate" : "2019-01-12T07:59:59.999Z" },
{ "_id" : "2", "startDate" : "2019-01-21T07:00:00.000Z", "endDate" : "2020-01-04T07:59:59.999Z" }
]
}